GOES-13 10.7 µm IR images + OSCAT surface scatterometer winds

Tropical Storm Debby formed in the eastern Gulf of Mexico on 23 June 2012 — Debby was the earliest “D”-named (4th storm of the season) Atlantic Basin tropical cyclone on record. GOES-13 10.7 µm IR channel images with an overlay of Oceansat-2 OSCAT surface scatterometer winds from the CIMSS Tropical Cyclones site (above) showed that Debby was embedded within a very broad cyclonic circulation that was present over the Gulf of Mexico — and Debby also formed over an area of high ocean heat content.

The low-level circulation center of Debby was generally exposed, but a large area of deep convection persisted within the eastern semi-circle of the storm. A number of Tropical Overshooting Tops were also seen associated with this deep convection (below).

GOES-13 10.7 µm IR images + Tropical Overshooting Tops

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR chnanel data (below) showed a detailed view of the low-level circulation center and the cold IR cloud tops of the deep convection.

Suomi NPP VIIRS 0.64 µm visible channel + 11.45 µm IR channel images

Abundant moisture was present over the entire Gulf of Mexico, as revealed by the MIMIC Total Prcipitable Water (TPW) product (below; click image to play animation). TPW values in excess of 60 mm (2.4 inches) were common.

MIMIC Total Precipitable Water product (click image to play animation)

During the following overnight hours, a comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel data (below) showed cloud top IR brightness temperatures as cold as -90º C (dark violet color enhancement), while the Day/Night Band image revealed a few bright white pixels indicating cloud illumination due to concentrated lightning activity. The bright lightning illumination pixels appeared to be “smeared” along the scanning direction of the VIIRS instrument. Also evident in the northwestern Gulf of Mexico were numerous small lights associated with extensive offshore drilling operations.

Suomi NPP VIIRS 0.7 µm Day/Night Band image + 11.45 µm IR image

During the afternoon hours of 24 June, another comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data (below) showed that some areas of deep convection had begun to develop into the northern semi-circle of the storm.

Suomi NPP VIIRS 0.64 µm visible channel + 11.45 µm IR channel images

===== 25 June Update =====

MODIS 11.0 µm IR, VIIRS 11.45 µm IR, and AVHRR 10.8 µm IR images

Even though the center of Tropical Storm Debby remained offshore, a large convective burst developed over the Florida Panhandle region on 25 June 2012. In the sequence of three 1-km resolution IR images (from the MODIS, VIIRS, and AVHRR instruments) shown above, the coldest cloud top IR brightness temperature was -91 C on the 16:21 UTC MODIS image.

The corresponding animation of 4-km resolution GOES-13 10.7 µm IR images is shown below .

GOES-13 10.7 µm IR images (click image to play animation)

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MODIS true-color image, Sea Surface Temperature product, and 0.65 µm visible channel image

AWIPS comparisons of a 250-meter resolution MODIS true-color Red/Green/Blue (RGB) image at 16:46 UTC on 21 June 2012 with the corresponding 1-km resolution MODIS Sea Surface Temperature product and 0.65 µm visible channel image (above) revealed the vivid signature of iron and/or copper rich runoff sediment in the near-shore waters of western Lake Superior following the historic heavy rainfall event of 19 June – 20 June 2012 (for more details on this event, see the Duluth National Weather Service).

A “before” (21 May 2012) and “after” (21 June 2012) true color image from the SSEC MODIS Today site (below) showed the dramatic change in appearance of the western Lake Superior near-shore waters.

MODIS true-color images (21 May 2012 and 21 June 2012)

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7-day total precipitation, percent of normal, and departure from normal

Maps of the total 7-day precipitation, percent of normal precipitation, and precipitation departure from normal (above) highlighted the extreme nature of the event in the Duluth region, but also showed the large amount of variability in precipitation across other portions of the Upper Midwest states during this period.

In particular, note the large southwest-to-northeast oriented swath across northeastern Nebraska, northwestern Iowa, southeastern South Dakota, and southwestern Minnesota (below): in this highly agricultural area, the stress on the crops within this rain-free swath was apparent on MODIS 0.65 µm visible imagery (lighter gray where the vegetation was less healthy), the MODIS Land Surface Temperature (LST) product (LST values in the upper 80s to mid 90s F, surrounded by LST values in the 70s F), and the Normalized Difference Vegetation Index (NDVI values as low as 0.43 in southwestern Minnesota, surrounded by NDVI values of 0.7 to 0.8 to the north and to the south where ample rainfall had been occurring).

MODIS 0.65 µm visible image, Land Surface Temperature product, and Normalized Difference Vegetation Index product

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GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (above; click image to play animation) revealed the interesting convergence of an undular bore (which was propagating northwestward) and a von Karman vortex street (which was moving southeastward, downwind of Guadeloupe Island) on 20 June 2012. Both of these features were likely traveling within the stable marine boundary layer.

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GOES Sounder Imagery during Filter Wheel Anomaly

On June 20, 2012, the GOES-13 Sounder Filter Wheel mechanism suffered an anomaly. The filter wheel moves the spectral filters into the optical path of sensed radiation. As a result of the anomaly, data quality was degraded starting at about 1248 UTC. Instrument recovery activities occurred at 1756 UTC on 20 June, and qualitatively the data returned to normal. Imager data were not affected.

GOES Sounder Imagery during Filter Wheel Anomaly

When GOES Sounder data are degraded, GOES Sounder Derived Product Imagery is also degraded. For example, the Precipitable Water image from 1746 UTC on June 20 is shown above. GOES-15 Sounder data returns over the western United States do not show the data dropouts characterized by the Filter Wheel Anomalies in GOES-13 over the eastern United States.

Filter Wheel anomalies have occurred in the past on GOES-12. GOES-10 Filter Wheel anomalies caused a data interruption on GOES-10 from Oct 14th to Nov 6th, 2008. GOES-8 also suffered from rare filter wheel anomaly issues (Link).

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